Eyes Flashcards
Eye anotomy
(fluids)
There are 2 areas of fluid which give the eyes their shape.
- Vitreous humor (back)
- Aqueous humor (front)
Eye anotomy (front)
Cornea - transparent layer protecting the eye on the ouside. Allows light to enter the eye and fall on th lense via iris
Iris - coloured area that changes size depending on the amount of light going throu it via the pupil. In low light, they enlarge. In bright less they are smaller.
Lens - located byhind the iris and changes change/stretches with assistance of ciliary muscles, to control focus. the greater the curvature, the greater the focus (occurs at a near object)
Eye anotomy (back)
Retina: Light focused by the lense on a light-sensitive membrane
In the Retina, there are Rods and Cones photoreceptors connected to nerve cells
the most sensitive area of the Retina is Fovea because it has lots of ‘cones’ only
Rods and cones are not distributed evenly
What are Rods
dark-seeing
help with peripheral vision
sensitive to movement
seeing in low light
not colour sensitive (only grey, blacks, whites)
located outside the foveal
What are Cones
Light seeing - help with seeing in bright light / daylight:
- colour sensitive
- seeing in detail
- distant objectives
located in the central section of the retina (foveal)
Visual interpretation
Retina converts the focused light into electrical impulses that reach the lower end of the brain and then routed to the visual vortex to interpret the info received from both eyes.
This info is then passed on to the cerebellum via the optic nerve, which helps us control movment and balance.
What is Field of View
it’s the portion of the world we see with each eye (monocular vision) when stationary
usually 120 degrees Horizonal
150 degrees vertical
What is the field of view when using binocular vision
there is an overlap of field of view at 60 degrees from the centre of the field
What is the blind spot
In the binocular vision in each eye there is an area in the retina without rodes or cones(light sensitive cell) ‘5 degrees blind spot’ - it’s usually where the optic nerve leaves the eyeball.
the info/image missing in one eye’s blindspot is compensated by what the other eye sees - hence you need binocular vision.
“must move your focus of attention frequently to scan your surroundings’
what is central vision
in the Fovea, there is an area of cone vision (1 degrees) that has the most visual acuity
Peripheral vision
area that detects movement but can’t distinguish details (you will see it best you move your sight to the sides, as opposed to centre in dark light)
what is binocular vision and its benefits
Binocular: using both eyes to focus
Benefits:
Eliminate risk of blindspots
Can see depth better: when looking at an object, each eye receives light from the object at different angles. The 2 images help the brain determine the distance of the object. The difference in both objects is greater when close vs far.
see in 3D
What kind of vision (binocular or monocular) gives us depth and distance
binocular
Types of depth and distance illusions
Parallax
head movements cause distant objects to appear to move relative to each other
Perspective
converging parallel
Relative size
Distant objects look small/closer objects look large
Relative motion
Distant objects appear to move slow/ closer objects appear to move fast
Overlapping motion
object in front of another appears closer
Aerial perspective
Distribution of light at a distance makes objects look blue
How to protect the eyes from bright light
Eyes take a wide range of light conditions ranging from light to dark
High energy lights - blue and ultraviolets found at high altitude
Bright light is dangerous due to high UV wavelength. The effectds are cumulative and can lead to blindness
Use 100% UV protective sunglasses
high quality optical glass
impact resistant
thin frames
reduce glare and increase contrast in the dark
avoid photosensitive glasses as they don’t adapt to changing lights
avoid polarised glasses as they can conceal important colours in the instruments you use
Affects of Dim light on the eye
DARK ADAPTATION
Dim lights reduce the resolution of objects, especially at a distance because cones don’t work in dark light and generally need brightt light to focus.
the pupils try to dilate to allow more light in (this takes seconds) but the Cones take 9 min and** rods take 30 min to fully adapt**
*anything affecting vision like hypoxia usually is more noticeable at night, even if below 10,000 ft)
Night vision can deteriorate at 4000 ft
*bright light inside affects vision at night
how to manage with dim lights
- avoid bright white light (strobes, flashing, landing lights) 30 min before flying at night.
- avoid white light even inside the cockpit
- move your eyes 10 degrees to the side of an object, so that the light hits the rodes area more than the cones. Rodes help focus on objects in dim light
use red light in cockpit - it has less effects on the retina compared to green and bue
when switching from bright to dark - close one eye whilst the other is open
Vision -
What is accommodation
ability of the eye to focus on close and distant objects
ie. far to close/close to far
deteriorates with age and tiredness
what is myopia
Reflective Error due to shape of the eye or power of the lens
short sightedness
can focus up close but not far
need concave lense to fix
hyperopia
long sightedness
can focus at a distance but not close
(ie reading)
need convex lens to correct
Use of corrective lenses by pilots
Avoid using reading lenses because distant objects will be blurred
Use half moon lenses
Use bifocal lenses (not vifocal lenses)
Visual system is comprised of 2 things:
optic nerve + visual vortex
what’s the visual vortex
part in the brain responsible for processing info received by the eyes - processes motion, colour and shape
function of the tear duct
washes the surfaces of the eye with antibiotic solution.
needs to be kept moist to help oxygen difuse thru
and protect from damage from dust particles
visual acuity
capacity of the eye to resolve detail (depends on density of photoreceptors) depending on distance
12 megapixel resoultion vs 3megapixedl
with more distance, the less detail you can resolve
where can alpha neumeric info be resolved
in the fovea because it’s the part of the retina that can process visual detail
which part of the retina is better for resolving objects at night
rods that help with peripheral vision can detect movement of objectts in dim light or at night
what are the 2 movements of the eye
Saccade and pursuit movements
explain the movement of the eye
Saccades are directed towards stationary targets to align our visual axis to the object
pursuit is directed at moving targets
our eyes combine both movements with no conscious
eyes move by 6 muscles
Normal acuity
ability to see 20/20 (6/6)
in snellen chart, what does 20/40 mean?
a person is able to read the letters at a visual acuity of 20 feet compared to a normal person who can read it at 40 feet - this is a near sighted person
factors affecting Visual Acuity
which angle of the eye you are seeing from
dark conditions
age
disease
dead photoreceptors
hypoxia
smoking, drinking, medication
short/near sightedness
external conditions (dust, weather, water, or anything that physically obscures object)
why avoid photochromic sungalsses
don’t respond to changing light conditions, especially going from light to dark
they require UV light to function
why avoid polarised glasses
adds polarising effects on screens and displays which hinders your visibility
what is empty field myopia
if the eye has nothing to focus on, it resumes a default focus 1 - 2 metres.
if you are looking at distant threats, you will be unable to see them at first and must refocus
Look at distant objects in the environment, distant or at the horizon or even your wingtips - should do continuous scanning
Detecting objects in the dark
1) the more the pupil enlarges, the less focus it has. It puts a lot of reliance on the lense to adjust focus
2)we have less rods near the fovea so hard to see objects i the dark in central view, so you may have to look at objects from the side a bit where there are more rods
Tips for look out
- involve** a degree of frequent eye movement **to cover blind spots
BUT frequent eye movement might stop you from detecting ‘relevant movement’
- move attention to one erea, then keep still for a period (to help detected movement), then move to next area. Make sue that your vield of vision at each stop overlaps the previously searched area by 10 degrees
- **you can be on a collision course with another aircraft because there is no apparent relative motion between you and the other aircraft. Aircraft will get bigger and bigger.
If you are flying 100 knots and aircraft is fying 500knots, then the rate of closure is 600knots (10nn per min)
the time you see the other aircraft depends on when you see the aircraft and the rate of closure.
If you see the aircraft at 1nm, you have 1/10th of a minute (6 seconds)
if you see the aircraft at 3nm, you you have 18 seconds
- **look at distant objects **in straight direction for focus
- **avoid empty field myopia **by consciously look at distant objects like a cloud, a wing tip otherwise your eyes will only focus at 1-2 m ahead and miss a distant aircraft
*be aware that in hazy conditons aircrafts whose edges are blurry/unclear may appear further than they really are.
LOOK OUT AT NIGHT
- need to rely on peripheral vision
- scan the sky more slowly than daylight
- look at objects from the side 10-20 degrees
what is scotopic vision
distinguish light and dark - ie rods
photobic vision
ability to detect colour - cones
Color blindness (photopic)
Inability of detecting some colour due to imperfection in the cones or absense of hte cones - usually red and green
dangerous because you can’t see certain lights like nav lights or lights from ATC tower
Ishihara cards
to test colour blindness
Refractive errors
defect in shape of the eyeball or deffects in the power of the lens
here the plane of focus does not align with the retina, therefore need corrective lenses to bring the focus on the retina
Astigmatism
imperfection in the shape of the cornea or lens. Causes uneven refractions of rays
so results in different optical power in different areas of the cornea or lens
difficult to resolve detail - image is distorted
can be corrected by lenses
Symptoms of astigmatism
sometimes no symptoms
but with age it can become common
can cause headaches, blurred vision, lack of focus, squinting to focus
Glaucoma
pressure on the retina impacting blood supply resulting in death of retina cells
happens suddenly and progress fast, by then treatment is too late — can cause lack of focus on details and blindness
can be medicated or surgery
caused with age
cataracts
clouding of the lenses of the both eyes at same time
slow and progressive - can cause blindness
caused by age or chronic exposure to UV lights
in some cases you need to remove lenses and replace with artificial ones
presbyopia
form of long sightedness but related to elasticity of the lense
causes difficulty in accommodation of near vison
can’t read small print in poor light or when tired
need lenses that don’t correct distant visioun but required for reading vision. Can use half moon convex in lower part of the lenses
Sight is very sensitive when?
during hypoxia, or under drugs/alchohol or meds
G force
How do eyes move?
Via the brain
3 Types of movements:
1) eyes are stationary but head moves
2) eyes move but head is stationary
3) both eyes move in harmony to track objects
what is double vision
when eye muscle coordination fails/ hindered due to fatigue
effects of glare
Pilot exposed to high intensity lights from all angles and is not protected from them.
also glare caused by bright environment and dark cockpit can make it hard to adjust quickly to read charts and instruments.
wear protective sunglasses as long as they don’t affect acuity
effects of flickering lights
caused by sequence of light and shade (ie movement of propellor) usually affects hilicopter pilots
causes uneasiness
should wear sunglasses
should cover eyes or window
Depth & distance perception
- Binocular vision helps
- clues from memory and experience that the eyes and brains use
- mathematical (ie size of object): bigger object appears closer
- Texture: the more visible the texture, the more close the object is.
Relative motion: closer objects appear to move fast compared to distant objects
Texture
1) on final approach as you near the runway, its texture appear to flow outwards in all directions. It helps you maintain a constant approach slope to the aiming point
2) as you approach **flare height for landing, the texture of runways or grass passing by teh cockpit beccomes noticelable **
3)In hazy conditions, its difficult to see edges and details or texture so objectics appear closer ( you might down down closer)
Visual illusions
images seen by the eyes are misinterpreted by the brain.
what we see in our brain isn’t the reality
Autokinesis
False expectation
Interpretting patterns
False horizone
Approaches: black hole, night approach, slope, size, obscuured
Autokinesis
usualy happens at night
when you stare at a light object in the dark background at stationary position but you think it’s moving. This is because you lose focus at night and your eye is trying to focus.
This confuses pilot and might thing the object afar is moving when it’s not.
move your eyes in normal scanning, look at your instruments, focus on distant objects briefly
false expectations
ex:
we expect a pencil to be smaller than a tree
but when both are seen next to each other in the same angular area of the retina, we assume the tree is further away.
A small image formed in the retina could be a distant rapid aircraft of a spec of dust
if you land at same runway, you are used to its width/length but if you land in a different runway, you are presented with different view even if the approach slope is correct
Interpretation of pattersn
our brain makes sense of patterns of lines but interpretation may not always be correct
ex:
windshield has rain
you are appraoching and you perceive the runway to be in a specific location becdause your eyes see it this way but in fact, it is in a different location because of the light refacting on the water in the windshield.
false horizon
cloud layers slope or angled lines seen at night may give a sense of horizon that is wrong
2 aircrafts at opposite ends of a sloping cloud look like they are on the same level
need check altitude and balance ball regularly
Runways slopes
If the runway is on an up-slope, it will appear longer. You will feel you are high on slope and will tend to** make a shallower approach**
If the runway is on an down-slope, it will appear shorter. You will feel you are low on slope and will tend to make a higher approach
runway size
**runway that is larger **than usual, will **appear close **than the reality
a runway that is smaller than usual will appear far than the reality
a wide runways, because of hte angle you view it in final stages of the approach, will cause illusion of being too low. **You will fly higher appraoch and overshoot/or land further after the runway threshold
**
a narrow runway, will causeillusion of being too high, and you might make contact with the runway earlier and harder. yOu will tend to fly a lower approach and land short
haze
you might be closer to the runway than you may appear to be
The night approach
Ideally use powered approach at night to ocntrol the lower rate of descent - here use PAPI
for correct tracking - try to ensure that the runway is symmetrical in the windshield
to guide you make the correct approach slope - look at the runway edge lights:
if only runway lights are used:
if you are too low, the lights intervals will be close
if you are too high, the ight intervals will be further
black hole approach
when approaching a runway that ight have its edge lights but not other lights from the surrounding environment or terrain..common in runways surrounded by desert, waterbodies
you might think you are higher than the reality
might make steep descends/lower approach
use ILS or VASI or rely on altimeter and vertical speed indicator to control slope and rate of descent
obscured approach
runnway obscured by snow for example, making depth and slope perception more difficult
during the night, at 10000ft, your visual acuity has decreased.
what to do?
use supplementary oxygen
Binocular cues
Depth perception:
using both eyes to get 2D images and form 3D images when you include the brain’s interpretation.
Retial disparity:
Depth perception at up to 60m.
Helps judge length of runway at up to 200 ft
using both eyes to get 2D images to form 3D images and the brain analyzes the difference to deduce distance.
Convergence
Produces depth info over 6-20 ft
when each eye moves inwards as an item gets closer and each eye sees an object from a different angle.
Binocular cues
(for short distances)
Depth perception:
using both eyes to get 2D images and form 3D images when you include the brain’s interpretation.
Retial disparity/steropsis:
Depth perception at up to 60m.
Helps judge length of runway at up to 200 ft
using both eyes to get 2D images to form 3D images and the brain analyzes the difference to deduce distance.
Convergence
Produces depth info over 6-20 ft
when each eye moves inwards as an item gets closer and each eye sees an object from a different angle.
Monocular vision
(for further distances)
Texture
Seeing extreme details mean items is close,
Seeing smooth surface mean items is far
Atmospheric/relative brightness:
items that are far are pale/blue
Motion Parallax:
when you are moving but stationary items at various distances appear to move at different speeds
Obstruction/overlap - objects covered by others look further away
Relative size/Retinal size: 2 items of same size, the closer one looks bigger
Linear perspective: more convergence, more distance
Height in visual field
if 2 items are on the same height relative to the angle of the observer, the item that occupies the retina spot the most is the ‘closer’ item
spatial orientation
misinterpretation of aircraft speed, altitude or position because of conflicting info from senses (vision, equillibrium and seat of the pants’
Even in case of spatial orientation…rely on your…
vision and instruments
how long does it take to adapt to light and darkness
10 seconds to light
30 min to darkness
pupil
regulates amount of light hitting the retina
contact lenses can only be worn if
pilot is short sighted (as in he can see close, but cannot see far and requires long distance correction)
contact lenses can cause issues in flight…
can dry up, cause itching, burning, etc
can increase corneal damage due to dehydration and mild hypoxia of the eye
they can dislodge and reduce visual acuity
usually good with peripheral vision than glasses
humidity doesn’t affection lenses
if you fly into clouds in IMC, which sense should you rely on
Vision
when scanning, how doesn the eye move and how is smooth vision achieved
the eye does jerky movements called ‘saccades’
smooth vision is achieved in the visual cortex of the brain
if you see thunderstorms, you should
lightning might provoke a residual image in your retina, appearing in your vision for few minutes
to adapt to this high level of light, turn up the cockpit lights
visual acuity at high altitude can be affected by
hypoxia and CO poisoning
smoking
anemea
What is the order of light frequency we see (colour)
ROYGBIV
Lowest frequency to Highest
Red
Orange
Yellow
Green
Blue
Indego
Violent
combination of all = white light
Lack of all = Blackness
what’s the % of info we process comes from
70% of info is visual from the eyes
Acuity
Clarity / ability to see detail
The main focus of detail occurs within **10-15 degrees **
Seeing detail is affected by:
hypoxia
atmosheric clarity
distance from viewer
countor of object
relative movement
amount of light present
contrast
field of view
120 degrees - left and right
150 degrees - up and down
overlap of 60 dgrees where bincolur view occurs
colour blind
subtle
can be detected by specialized tests
Night vision affected by
Hypoxia = 5000 ft
age, smoking, cabin pressure, drinking = 8000+ft
compensatory stage = 15,000 ft
what should you do at night with cockpit light
**increase the lighting **to also prevent low vigilence
cockpit uses RED light as it affects Rods less than white light
how do we see
—>50% of info enters the eyes
1) eye does jerky quick movements (saccade) and will (fixate) on an item =fraction of a second
2) eyes take 30-40 images per second which is what detects movement
3)2D images
–> 50% of info processed by braind
3) brain takes 1/50th of a second to process
–3D is learnt/created by. the brains
–expectectations and expereince is used
–brain fills the gaps
–illusions
glare
too much light entering pupils
red eye
when not all the light can be absorbed and some is reflected back
old vs young people
old people need twice as much light than young people
Visual Purples
these are rhodpsin in the Rods that help build up from light to dark in 30 min
need vitamin A
Rods and Short vs Long wavelength
Rods can detect Blue objects instead of Red because blue has ‘short wave length’
rods are sensitive to shorter wavelength
Photopic
Scotopic
Mescopic
Photopic - cones/central vision used in high intensity light
scotopic - rods/used for peripheral vision (see shades of grey) in low light
Mescopic: using rods and cones together but cones start to reduce colour perception. During dawn, dusk, full moon
cornea bends light by %?
Lens bends light by %?
70%
30%
function of the lens
helps with accommodation - focusing light into the retina
what damage can the eye have
cornea is affected by** lack of humidity** (dries up) esp if wearing contacts
also the lens can be damaged by lack of humidity but also can get dislodged by g+ foce and rubbing
hypoxia
decompression - causes bubbles to form under the cornea
ciliary muscles
help keep the lense focused
can get tired from too much focus
pupils
control how much light enters
In low lights
big pupils = high depth of field = seeing less sharp or focused
in high light
small pupils = low depth of fiedl = seeing sharp/focused
defective vision
Hypermytopia:
eyeball is short. image reflected behind retina. Longsightedness/farsightedness. can see far but not close
Convex lens required
myopia:
eyeball is long. image reflected infront retina. shortsightedness. can see close but not far. Concave lens required
Night myopia
myopia but see even better at night
Presobypia
A form of hypertopia where seeing close is difficult
hardening of lens. lower accommodation
comes with age
redlight presobypia
cannot see close/small intrustment print in red cockpit light
cataract - opague lens
glaucoma:
increase pressure of liquid in eyeball
interferes with accommodation
progressive narrowing of field of vision
astigmatisation: uneven curvurture of the lense . fixed with cylindriacal lense
DERP
Design eye reference point
system/standard put in place to ensure you are sitting incockpit with best visibility of the outside and inside while making as head movements as possible
sunglasses
Must:
abosorb most of visible light -85%
eliminate glare
do not decrease visual acuity
absorb UV and IR radiation
**ideally :
**neutral-grey
non polaraized
not photochromic (take 30 min bleaching time to adapt, can conceal instruments, may absorb more light then they should, rely on UV light which is blocked by windscreen)
Wet winshield/prismatic effect
looking below at wet part, makes objects look Higher or Closer
Rain
Makes you feel closer
forces low approach
reflection on windshield
creates false horizon
white out
when you see dark object with no shadow, background, horizon or anything
so you lose depth perception
fog/haze
objects look far
blackhole/Kraft
dark terrain with little lights
make you feel higher and further
so you make steep approach and land short
upslope and downslope runway
Upslope:
feels like you are high
tend to undershoot/make low approach
Downslope
feel like you are low
tend to do high approach/overshoot
Wide and narrow
Wide:
Feels low
high approach
Narrow
feels high
low approach
bright light
makes you feel low
so you do high approach
Mountain terrain
hard to fly level due to different sloping ground
